High pressure reinforced hydraulic hose is typically used on a variety of fluid power operated machines, such as earth-moving machines, to provide a flexible connection between several moving parts of a hydraulic circuit employed on or within the machine. Such hoses may include a hollow polymeric inner tube on which successive cylindrical layers of reinforcing material, such as wire or textile, are concentrically applied to contain the radial and axial pressures developed within the inner tube.
Many applications are demanding hose constructions with both high burst strength and long term fatigue resistance. Using conventional technology, the burst strength of a hose design may be increased by adding additional reinforcing material and/or layers, a practice which is generally discouraged because of its negative impact on the flexibility of the hose, or by universally increasing the tensile strength of each layer of reinforcement material, which may come at the expense of hose fatigue resistance.
To determine the robustness of a hose design, a hose manufacturer typically performs, among other tests, an impulse test and a burst test on the hose. An impulse test measures a hose design's resistance to fatigue failure by cyclically subjecting the hose to hydraulic pressure. A burst test, on the other hand, is a destructive hydraulic test employed to determine the ultimate strength of a hose by uniformly increasing internal pressure until failure. Based on these and other tests, a manufacturer can estimate a hose life that can be used to determine when a hose has reached the end of its life and may require replacing.
In some circumstances, it is desirable to detect, in a non-destructive and non-disruptive manner a likelihood of failure of a hydraulic hose. One solution providing this capability is discussed in U.S. Pat. No. 7,555,936, and discloses connecting a monitor circuit between two parallel, at least partially-conductive layers of a hose wall. A change in an electrical property observed by that monitor circuit may indicate a change in a property of the hose wall structure that might indicate impending failure of the hose wall.
To determine whether changes in electrical properties of a hose assembly have occurred, an electrical circuit is applied to the conductive layers of the hose wall. This may be accomplished through use of spring-style contacts, or otherwise pressing electrical contacts into the hose wall at a location where the conductive layer of interest is exposed. However, such an arrangement has drawbacks. For example, it can be difficult to obtain a reliable electrical connection between the contacts associated with the electrical circuit and the hose layers. Vibrations or stress on the hose can cause damage to these contacts as well, which may wear the contacts quickly. Additionally, due to exposure to environmental conditions (heat, cold, moisture, dirt, etc.), spring-type electrical contacts can corrode or otherwise have their electrical connection interrupted by debris, thereby weakening or disrupting the connection between the electrical circuit and the conductive layer of the hose. This can cause electrical disconnection of the electrical circuit from the conductive layers, thereby either triggering a fault in the circuit or falsely detecting degradation of the hose itself.
For these and other reasons, improvements are desirable.